(6) Though the roots of _Sigillaria_ bear some resemblance to the rhizomes of certain aquatic plants, yet structurally they have much resemblance to the roots of Cycads, which the stems also resemble. Further, the _Sigillariæ_ grew on the same soils which supported conifers, _Lepidodendra_, _Cordaites_, and ferns, plants which could not have grown in water. Again, with the exception, perhaps, of some _Pinnulariæ_ and _Asterophyllites_, and Rhizocarpean spores, there is a remarkable absence from the coal measures of any form of properly aquatic vegetation. (7) The occasional occurrence of marine or brackish-water animals in the roofs of coal beds, or even in the coal itself, affords no evidence of subaqueous accumulation, since the same thing occurs in the case of modern submarine forests. Such facts merely imply that portions of the areas of coal accumulation were liable to inundation of a character so temporary as not finally to close the process, as happened when at last a roof shale was deposited by water over the coal. Cannel coals and bituminous shales holding mussel-like shells, fish scales, etc., imply the existence sometimes for long periods of ponds, lakes or lagoons in the coal swamps, but ordinary coal did not accumulate in these. It is in the cannels and similar subaqueous coals that the macrospores which I attribute in great part to aquatic plants, allied to modern Salvinia, etc., are chiefly found.[115] [115] "Geological History of Plants," _Bulletin Chicago Academy of Sciences_, 1886. For these and other reasons, some of which are more fully stated in the papers referred to, while I admit that the areas of coal accumulation were frequently submerged, I must maintain that the true coal is a subaërial accumulation by vegetable growth on soils wet and swampy, it is true, but not submerged. I would add the further consideration, already urged elsewhere, that in the case of the fossil forests associated with the coal, the conditions of submergence and silting-up which have preserved the trees as fossils, must have been precisely those which were fatal to their existence as living plants, a fact sufficiently evident to us in the case of modern submarine forests, but often overlooked by the framers of theories of the accumulation of coal.